strange noise rpm change - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 28 (permalink) Old 09-03-2015, 05:06 PM Thread Starter
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strange noise rpm change

i just got a 95 vn750 when i got it it was not running needed a stator fix that fired it up for the first time and cranks right up idles good ease on the throttle and at around 3000 rpm it makes a weird noise that sounds like it is coming from exhaust and the rpm jumps a little. ready to take it for a test drive but want to make sure it is nothing serious
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post #2 of 28 (permalink) Old 09-03-2015, 05:14 PM
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It could be an exhaust leak if you had the pipes off.

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post #3 of 28 (permalink) Old 09-03-2015, 05:43 PM Thread Starter
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I haven't had pipes off I did think that I have a video but can't figure out to post it
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post #4 of 28 (permalink) Old 09-03-2015, 06:39 PM Thread Starter
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post #5 of 28 (permalink) Old 09-03-2015, 06:46 PM
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sounds like the cam chains slapping really bad. if they flop enough, it could cause a miss (due to improper valve timing). also, if the chains are slapping, you will wear the sprockets out prematurely

another to thing to check, is all 4 plugs, wires. could have a loose plug, or a wire arcing to ground.

one other thing, if its trying to backfire thru the carbs, it could sound similar to that

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post #6 of 28 (permalink) Old 09-03-2015, 06:52 PM Thread Starter
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If it is the cam chains anything u can do for that Bike don't have that many miles on it
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post #7 of 28 (permalink) Old 09-03-2015, 06:58 PM Thread Starter
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It has been sitting a little while
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post #8 of 28 (permalink) Old 09-03-2015, 11:00 PM
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Sounds like maybe it's only running on one cylinder, until you get to 3000rpm and then it sounds like the dead cylinder is trying to fire some. Does it pick up rpm on it's own when you hear that sound?

See if one pipe is a lot cooler than the other, have to check toward the front because the exhaust mixes in the 'goat's belly' just ahead of the mufflers.

Could try pulling both plug wires from one cylinder. If it starts but there's no change in power, you have one cyl not firing. If it doesn't start, the other cylinder is the one with the problem.

Another test, but a bit tricky to do sometimes ... the cylinder short test. You remove a plug wire, then with the engine idling, you touch the wire back onto the plug. If the cylinder is firing, the idle will change. No change = dead cylinder. Except on this engine, we have two plug wires per cylinder, so pull both wires, then touch one back to the plug. The big trick is not getting the chit shocked out of you.

Not sure I'm hearing chain tensioners. I think what I heard could be the problem cylinder trying to fire. But it also sounds like what I heard when I had a sticky valve, which is also a possibility on yours. I hear a lot better when I can stand beside the engine.

If it is a cylinder misfiring, it could also be a fuel problem instead of spark.

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post #9 of 28 (permalink) Old 09-04-2015, 08:49 AM
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spock, agree on all you said, I didnt think of a dead jug until you said it.

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post #10 of 28 (permalink) Old 09-04-2015, 11:09 AM
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I'm with spock on this.

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